Recently, novel fine processing technologies are being developed with increase in the degree of integration and the performance of semiconductor integration circuits (herein after, referred to as LSI). Also a chemical mechanical polishing (herein after, referred to as CMP) method is one of these technologies, and is a technology frequently used in flattening of an inter layer insulating film, formation of a metal plug and formation of implanted wiring in an LSI production process, particularly, a multi-layer wiring formation process. This technology is disclosed, for example, in U.S. Pat. No. 4,944,836.
Recently, for increasing the performance of LSI, utilization of copper and copper alloy has been tried as a conductive substance of a wiring material. However, it is difficult to finely process copper and copper alloy by a conventional dry etching method frequently used in formation of aluminum alloy wiring. Therefore, there is mainly adopted what is called damascene method in which a thin film of copper or copper alloy is piled and implanted on an insulating film on which trenches have been previously formed, and the above-mentioned thin film on portions other than the trench portions is removed by CMP to form implanted wiring. This technology is disclosed in, for example, Japanese Patent Application Laid-Open (JP-A) No. H2-278822.
In a general metal CMP method of polishing a metal for wiring portions such as copper, copper alloy and the like, polishing cloth (pad) is pasted on a polishing plate (platen) in the form of disc, the surface of the substrate on which a metal film has been formed is pressed to the surface of the polishing cloth while wetting the surface of the polishing cloth with polishing slurry for metal, and the polishing plate is rotated under condition of given pressure applied to the metal film from the rear surface of the polishing cloth (herein after, referred to as polishing pressure), to remove the metal film at a convex part by relative mechanical friction between the polishing slurry and the convex part of the metal film.
Polishing slurry for metal used for CMP is in general composed of an oxidizer and abrasive, and if necessary, a metal oxide dissolving agent and a protective film formation agent are further added. It is believed a basic mechanism to first oxidize the surface of a metal film with an oxidizer, and scrape off its oxidized surface with abrasive. The oxidized layer on the metal surface at a concave portion does not contact significantly with a polishing pad and an effect of scraping off with abrasive is not exerted on the surface, consequently, the metal layer at a convex portion is removed with progress of CMP, leading to flattening of the surface of the substrate. The details of this are disclosed in Journal of Electrochemical Society, vol. 138, No. 11 (1991), pp. 3460 to 3464.
As a method of enhancing the polishing speed by CMP, it is the effective to add a metal oxide dissolving agent. The reason for this is interpreted that if particles of a metal oxide scraped off by abrasive are dissolved (herein after, referred to as etching), an effect of scraping off with abrasive increases. Though the polishing speed by CMP is improved by addition of a metal oxide dissolving agent, when, on the other hand, also an oxide layer on the surface of a metal film at a concave portion is etched to expose the surface of the metal film, the surface of the metal film is further oxidized with the oxidizer, and by repetition of this procedure, etching of the metal film at a concave portion progresses. Consequently, a phenomenon of formation of depression in the form of dish at the central portion of the surface of implanted metal wiring after polishing (herein after, referred to as dishing) occurs, deteriorating the flattening effect.
For preventing this, a protective film formation agent is further added. The protective film formation agent forms a protective film on an oxide layer of the surface of a metal film, and resultantly prevents dissolution of the oxide layer into polishing slurry. It is desired that this protective film can be easily scraped off by abrasive and does not decrease the polishing speed by CMP.
For suppressing corrosion during polishing and dishing of copper or copper alloy and for forming LSI wiring of high reliability, there is suggested a method of using polishing slurry for CMP containing BTA as a protective film formation agent and a metal oxide dissolving agent composed of amidesulfuric acid or aminoacetic acid such as glycine and the like. This technology is described, for example, in Japanese Patent Application Laid-open No. 8-83780.
In formation of metal implanting such as formation of damascene wirings of copper, copper alloy and the like and formation plug wirings of tungsten and the like, when the speed of polishing a silicon dioxide film which is an inter layer insulating film formed on parts other than the implanting formation parts is also large, thinning in which the thickness of wirings also including the inter layer insulating film decreases occurs. As a result, increase in wiring resistance occurs, therefore, a property is required in which the polishing speed of a silicon dioxide film is sufficiently small in comparison with the metal film to be polished. For suppressing the polishing speed of silicon dioxide by an anion generated by dissociation of an acid, there is suggested a method of increasing pH of polishing slurry more than pKa-0.5. This technology is described in, for example, Japanese Patent Publication No. 2819196.
On the other hand, as the lower layer of a metal for wiring part such as copper, copper alloy and the like, a conductor layer of, for example, a tantalum compound such as tantalum, tantalum alloy, tantalum nitride and the like is formed, as a barrier conductor layer for preventing diffusion of copper into an inter layer insulating film and improving close adherence with this (herein after, referred to as barrier layer). Therefore, on parts other than wiring parts of implanting copper or copper alloy, an exposed barrier layer should be removed by CMP. However, the conductor of this barrier layer has high hardness as compared with copper or copper alloy, consequently, sufficient polishing speed is not obtained and its flattening property deteriorates in may cases even if a polishing material for copper or copper alloy is combined. Therefore, a two-stage polishing method composed of a first process of polishing a metal for wiring and a second process of polishing a barrier layer is investigated.
In the second process of polishing a barrier layer of the above-mentioned two-stage polishing method, polishing of an inter layer insulating film, for example, silicon dioxide, or organosilicate glass using trimethylsilane as a starting material which is a Low-k (low permittivity) film, or whole aromatic ring-based Low-k film is required in some cases for flattening. In this case, there is mentioned a method of polishing while maintaining the flatness of the surface of a barrier layer, a metal for wiring and an inter layer insulating film by approximately equalizing the polishing speed of a barrier layer and metal for wiring part and the polishing speed of an inter layer insulating film so that the polished surface is flat when all of the inter layer insulating film is exposed.
For increasing the polishing speed of an inter layer insulating film corresponding to the polishing speed of a barrier layer and metal for wiring part, there is envisaged, for example, to increase the size of abrasives in polishing slurry for conductor of a barrier layer, however, there is a problem that scratch occurring on copper or copper alloy and an oxide film, causing a poor electric property.
Such a poor electric property is generated also by poor washing after polishing by CMP. On the other hand, there is a problem of occurrence of a short-cut defect since the copper residue on high density wiring parts cannot be removed in a CMP process.
The present invention provides polishing slurry giving a polished surface having high flatness in view of the above-mentioned problems. Further, there is provided polishing slurry by which the polishing speed of an inter layer insulating film is as fast as the polishing speed of a barrier layer and a metal for wiring part. By this polishing slurry, the speed of polishing a wiring part can be controlled without decreasing the speed of polishing a barrier layer. Metal residue and scratches after polishing can be suppressed. Further, the present invention provides a polishing method in production of a semiconductor device excellent in fineness, film thinness, dimension precision and electric property, and having high reliability, and requiring low cost.